1. Field of the Invention
The present invention relates to a high-frequency module used in a microwave band or a millimeter wave band, such as a resonator, a filter, or an oscillator, and to a method of adjusting the characteristic thereof and a transmitter-receiver including the high-frequency module.
2. Description of the Related Art
Each of the following references: (1) Japanese Unexamined Patent Application Publication No. 5-129810, (2) Japanese Unexamined Patent Application Publication No. 5-129812, and (3) Japanese Unexamined Patent Application Publication No. 2001-292028 discloses a high-frequency module whose electrical characteristic is adjusted by trimming.
In (1), resonance frequency is adjusted by forming a through hole or a non-through hole in a resonator so that a laser beam is radiated thereto, or by removing a ground plane, a dielectric portion, and a central conductor by sandblasting.
In (2), a window of a metallic substrate is open in the back side of a sub-strip line such that the entire microstrip line is exposed. In this configuration, the resonance frequency of a dielectric resonator element is changed by removing the back surface of the microstrip line through that window.
In (3), frequency is adjusted in the following way in a voltage-controlled oscillator. That is, a microstrip line resonator is formed on a dielectric substrate and a case is attached on the dielectric substrate. Then, a laser beam is radiated to the back surface of the dielectric substrate so as to trim a strip electrode.
In (1) and (2), the size of the hole and window used for adjustment is not limited. Therefore, in a high-frequency band, such as a millimeter wave band, the module may be externally affected significantly. Also, since the output of a signal leaks out, entire power efficiency may be reduced.
In the adjustment method of (3), the strip electrode to be trimmed cannot be seen directly. Thus, it is very difficult to adjust the amount of trimming in a high-frequency module of a millimeter wave band.